I understand what you're trying to do but I think this change is too drastic for existing users. I take it you want to promote collections rather than individual mods. You have a dilemma of angry existing users and your need to push new users into collections. I have a solution.
1. Revert everything to old layout.
2. On signing up of new users make "collections view" the default. Allow a site preference option to choose "mods view".
3. Rename "collections" to "Quick Start", explain what it does when users first register.
4. A big huge unmistakeable pulsating button to toggle between the two, displayed prominently.